THE SITE OF VERREBROEK ‘DOK’ AND ITS CONTRIBUTION TO THE OF THE MESOLITHIC IN THE LOW COUNTRIES

Mark J Y Van Strydonck1,2 • Philippe Crombé3 • Ann Maes1

ABSTRACT. The wetland site of Verrebroek “Dok” situated in northern Belgium is one of the largest and best dated loca- tions of Mesolithic material in northwestern Europe. Salvage excavations organized since 1992 at this large, unstratified open- air settlement have revealed more than 50 spatially independent artifact concentrations with traces of numerous fireplaces. Single entity dating of charred hazelnut shells from surface-hearths and charcoal from hearth-pits was used to obtain infor- mation not only on the sites duration, but also on the relation between the surface hearths and the hearth-pits. The dates were also used to look at discrepancies between the radiocarbon and the typo-chronology of the lithic artifacts.

INTRODUCTION

Problems in Dating Stone-Age Settlements on Sandy Soils In a recent article (Crombé et al. 1999) we discussed the problems of absolutely dating Final Pale- olithic and Mesolithic camp sites situated on highly bioturbed sandy soils within the Low Countries. The origin of this dating problem is caused by: 1) a bad or doubtful spatial association of the dated sample and the lithic industry, 2) dislocation caused by bioturbation processes, 3) multiple site occu- pation, and/or 4) inbuilt age of the dating material. The use of single pieces of charred hazelnut shells (CH) from surface-hearths (SH) and single charcoal (CC) fragments from hearth-pits (HP) was rec- ommended as a protocol for future dating projects in the sandy area of northwestern Europe. Between 1998 and now further testing has been done on the Mesolithic site of Verrebroek in view of refining the proposed dating strategy. The results of this project will be discussed in the present paper.

SITE DESCRIPTION The site of Verrebroek “Dok” (51°16′00′′N, 4°12′42′′E) is situated in the polder area of Flanders on the extreme east end of a late glacial aeolian sandy dune ridge (ca. 80 km long, ca. 2–3 km wide) that blocks the north part of the Plain of the Flemish Valley. This sandy elevation in the lowlands of Flanders was intensively used during the stone ages, in particular during the Final Paleolithic and the Mesolithic, as can be demonstrated by the presence of numerous sites (Crombé 1998b:95–102). Sites situated on the eastern extremity of this sand ridge, such as the important sites of Melsele “Hof ten Damme” (Van Roeyen et al. 1992; Van Strydonck et al. 1995), Verrebroek “Dok” (Crombé et al. in press) and the recently discovered site of Doel (Crombé et al. 2000), are the only ones that are well-preserved. Peat and alluvial deposits from the river Scheldt have protected these sites against erosion and destruction. Since 1992 the Department of of the Ghent University is excavating the site of Verre- broek “Dok”. Actually about 6000 m² have been investigated, corresponding to around 20% of the entire site-surface. The excavations revealed at least 50 artifact concentrations of varying size and composition. The smallest units cover 1–2 m², the largest ones 50–100 m². The majority of units however is smaller than 10–15 m². All excavated units mainly consist of stone artifacts, mostly made of local flint of inferior quality. Some units also yielded a certain amount of exotic raw materials,

1Royal Institute for Cultural Heritage, Jubelpark 1, B-1000 Brussels, Belgium 2Corresponding author. Email: [email protected]. 3Postdoctoral Fellow of the Fund for Scientific Research-Flanders, Department of Archaeology and Ancient of Europe, Ghent University, Blandijnberg 2, B-9000 Ghent, Belgium

© 2001 by the Arizona Board of Regents on behalf of the University of Arizona RADIOCARBON, Vol 43, Nr 2B, 2001, p 997–1005 Proceedings of the 17th International 14C Conference, edited by I Carmi and E Boaretto 997 998 M J Y Van Strydonck et al.

Figure 1 Schematic and preliminary draft of the artifact units excavated between 1997 and 1999. 1. hearth-pits; 2. bone clusters; 3. surface-hearths; 4. artifact units; 5. Medieval ditches. such as quartzites and sandstones. Due to unfavorable preservation conditions (Ph-value and oxida- tion degree) organic material is extremely badly preserved on the site. It appears that only carbon- ized organic residue, such as charcoal, hazelnut shells and bones, is preserved. Besides numerous natural features (e.g. tree-falls) three main archaeological features are found at Verrebroek (Figure 1 above): i) surface-hearths (SH), ii) hearth-pits (HP), and iii) pits. Due to later soil processes (e.g. formation of a heather podzol) the SH are no longer preserved as real soil features. Their position can only be deduced by the presence of concentrations of burnt artifacts and ecofacts. Associated charcoal was never observed. SH are always found within the boundaries of artifact concentrations associated with different types of tools (mainly microliths and scrapers) and lithic knapping waste (flakes, bladelets, chips, cores). It thus appears that these SH were used for various purposes (warming, cooking, melting of resin, etc.) and therefore can be interpreted as domestic hearths. On a spatial level it could be observed that all units smaller than 15–20 m² gener- ally display one single SH, whereas larger units posses more SH, usually two but occasionally up to four and even five specimens (e.g. C.14, C.22, C.40, C.44). It is questionable whether the latter are all synchronous (see below). Site of Verrebok “Dok” 999

The HP (12 examples) on the other hand are visible in the soil as black, charcoal rich, three-dimen- sional structures of 0.50–0.70 m in diameter and 0.35–0.50 m deep. Most HP are located within the boundaries of the artifact units, either in the center or near the periphery. Only few pits are found iso- lated from the artifact units. Contrary to the SH, HP have a very restricted distribution as they are only found in the SW part of the excavated area. This part formerly corresponded to one of the high- est grounds of the landscape. The filling of these HP mainly consists of CC fragments with Pinus as the dominant species, but also Quercus and Corylus (Louwagie et al. in press) were found. Lithics and CH only occur occasionally and in very small amounts. So far burnt bone fragments have not been found in HP. In two units (C.22 and C.14) vague traces of shallow pits filled with numerous CH, in some cases associated with CC, were noticed. At present it is not yet clear how to interpret these features, but one cannot exclude that it concerns remains of shallow hearths used for the roasting of hazelnuts or small storage-pits.

SAMPLE SELECTION AND TESTING Only single entities were dated. Each dated sample consisted of either one piece of CH from a SH or one piece of CC from a HP. Generally each feature was dated once. Some SH however were dated by more than one sample to obtain a better precision. This was the case for all features that were dated between 1992 and 1994 (Crombé 1998b:20–2) because some of the earliest AMS dates had very large standard deviations. Multiple dating on different CH samples was also done on some extremely large SH (e.g. in units C.17 and C.22) in order to verify their chronological homogeneity. Furthermore some HP were also dated several for methodological purposes (see below). All dated samples were cleaned using the acid-base-acid method, converted into graphite and mea- sured by AMS. Since some of the CH samples were badly preserved and some dates deviated largely from the bulk of the measurements it was feared that humic acid infiltration from the overlaying peat layer altered some of the CH dates. To clarify this the efficiency of the pretreatment was tested in two ways. At first a duplo sample from unit C.17 was dated after a repeated pretreatment (Table 1). Furthermore a larger CH sample, containing different individual shells, from unit C.22 (SH.2) was pretreated several times and the different residues as well as the soluble fractions were dated (Table 2). These tests demonstrate that the ABA method was sufficient to clean the samples. Judging by the small size of most HP only a limited “old-wood-effect” on the CC was expected. This was confirmed by dating determined branch and trunk wood from HP.66. It must however be admit- ted that anthracologically the term trunk wood is already applied to wood with a diameter exceeding 5 cm (Crombé et al. 1999). Dating different wood species within HP.91 revealed that the HP were, as expected, most probably only used once within a limited period and that no intrusive or residual CC was present in the pits. Two CC samples (UtC-3450: 8700 ± 100 BP from unit C.6 and UtC-3443: 7700 ± 100 BP from unit C.10) were rejected because soil analysis indicated that they originate from presumed natural pits. The above tests show that the CH as well as the CC samples are reliable and do date respectively the SH and the HP so that there is a close chronological connection between the 14C event and the human event (Van Strydonck et al. 1999). 1000 M J Y Van Strydonck et al.

Table 1 Radiocarbon dates from Verrebroek “Dok” 14C age δ13C Cultural Unit Structure Referencea (yr BP) (O) Sample materialb association C.1 SH. UtC-3915 9110 ± 65 −23.0 CH Beuronian A C.2.1 SH. UtC-3445 9100 ± 130 −25.4 CH Beuronian A C.2.1 SH. UtC-8398 9265 ± 40 −23.2 CH Beuronian A C.2.2 SH. UtC-3436 9130 ± 170 −26.8 CH Beuronian C C.2.2 SH. UtC-8391 8850 ± 50 −23.7 CH Beuronian C C.4 SH. UtC-8397 9065 ± 40 −21.6 CH Beuronian A C.5.2 SH. UtC-2743 9000 ± 190 −23.7 CH C.5.2 SH. UtC-8396 8795 ± 40 −23.8 CH C.6 Pit 16 UtC-3439 9150 ± 100 −26.9 CH Beuronian C C.6 SH. UtC-8961 9165 ± 45 −24.2 CH Beuronian C C.7 Pit 14 UtC-3451 9120 ± 120 −25.0 CH Beuronian C C.7 SH. UtC-8395 9015 ± 40 −26.4 CH Beuronian C C.9 SH. UtC-7851 9130 ± 75 −26.2 CH Beuronian C C.10 SH. UtC-2744 8920 ± 130 −26.1 CH Beuronian B C.10 Pit 23 UtC-3444 8920 ± 100 −24.3 CH Beuronian B C.10 SH. UtC-8394 8835 ± 40 −27.1 CH Beuronian B C.14 SH.1 UtC-7046 9100 ± 60 −25.6 CH Beuronian A C.14 SH.2 UtC-7045 9230 ± 50 −24.3 CH Beuronian A C.14 SH.3 UtC-7252 8750 ± 40 −23.9 CH Beuronian B C.14 SH.4 UtC-9222 8400 ± 60 −27.4 CH C.14 SH.5 UtC-9223 9080 ± 60 −23.9 CH C.14 Pit 90 UtC-9418 9060 ± 70 −24.5 CH C.14 Pit 89 UtC-9225 9270 ± 60 −23.0 CH C.14 SH.6 UtC-9419 9070 ± 70 −24.6 CH C.14 HP.88 UtC-9446 8230 ± 70 −25.5 CC Pinus branchwood C.16 SH. UtC-7117 8850 ± 40 −23.4 CH Beuronian B C.17 SH. UtC-7118 8930 ± 60 −25.4 CH C.17 SH. UtC-7120 9270 ± 50 −25.2 CH C.17 SH. UtC-7119 9280 ± 50 −23.3 CH UtC-7047 6260 ± 50 −25.5 CH after 1 pretreatment C.17 SH. UtC-7941 6290 ± 40 −25.5 CH after 2 pretreatments C.18 SH. UtC-9224 9160 ± 60 −27.1 CH Beuronian A C.19 SH. UtC-8392 8975 ± 40 −22.8 CH C.20 HP.66 UtC-9453 9100 ± 70 −27.8 CH C.20 HP.66 UtC-9452 8200 ± 70 −25.3 CC Pinus branchwood C.20 HP.66 UtC-9451 8190 ± 70 −24.5 CC Pinus trunkwood C.20 HP.67 UtC-9444 8390 ± 60 −24.8 CC Pinus branchwood C.20 HP.68 UtC-9443 8500 ± 60 −25.6 CC Pinus branchwood C.20 HP.70 UtC-9442 8450 ± 60 −25.6 CC Pinus branchwood C.20 HP.73 UtC-9447 8530 ± 60 −26.7 CC Quercus branchwood C.20 HP.92 UtC-9445 8330 ± 60 −22.6 CC Pinus branchwood C.21 SH. UtC-8390 9200 ± 40 −23.5 CH C.21 HP.91 UtC-9448 8250 ± 70 −24.5 CC Pinus branchwood C.21 HP.91 UtC-9449 8320 ± 60 −25.3 CC Quercus large fragment C.21 HP.91 UtC-9450 8330 ± 70 −25.1 CC Corylus large fragment C.22 SH.1 UtC-8388 8755 ± 40 −26.0 CH C.22 Pit/SH.2 UtC-8389 9310 ± 40 −23.1 CH C.22 SH.2 UtC-8393 9210 ± 40 −25.2 CH Site of Verrebok “Dok” 1001

Table 1 Radiocarbon dates from Verrebroek “Dok” (Continued) 14C age δ13C Cultural Unit Structure Referencea (yr BP) (O) Sample materialb association C.22 SH.2 UtC-9438 9290 ± 80 −26.0 CH after 2 pretreatments C.23 SH. UtC-9228 9020 ± 60 −26.0 CH C.26 SH. UtC-9227 8900 ± 60 −23.4 CH C.27 SH. UtC-9454 8790 ± 60 −24.4 CH C.28 SH.1 UtC-9226 8810 ± 60 −26.0 CH C.28 SH.2 UtC-9433 8800 ± 80 −25.8 CH C.33 SH. UtC-9456 9050 ± 70 −26.1 CH C.34 SH. UtC-9455 7720 ± 60 −24.2 CH C.35 SH. UtC-9457 8650 ± 60 −28.4 CH C.36 SH.1 NZA-11011 9190 ± 60 −24.7 CH C.36 SH.2 NZA-11247 8525 ± 60 −23.2 CH C.37 SH. NZA-11022 9490 ± 60 −27.3 CH C.38 SH. NZA-11016 9420 ± 60 −25.7 CH C.39 SH. NZA-11015 8900 ± 90 −22.5 CH C.40 SH.1 NZA-11024 9160 ± 60 −23.7 CH C.40 SH.2 NZA-11009 8660 ± 60 −26.7 CH C.41 SH. NZA-11012 9180 ± 60 −25.2 CH C.44 SH.1 NZA-11010 9200 ± 60 −23.0 CH C.44 SH.2 NZA-11025 8800 ± 60 −26.4 CH C.44 SH.3 NZA-11017 8790 ± 60 −26.5 CH C.44 SH.4 NZA-11248 8755 ± 85 −24.4 CH C.45 SH. NZA-11250 8685 ± 55 −25.7 CH C.46 SH. NZA-11023 7020 ± 60 −24.9 CH C.49 SH. NZA-11249 8675 ± 55 −23.7 CH aSamples prepared at the Royal Institute of Cultural Heritage, Brussels and measured at the Van de Graaff laboratory, Utrecht, the Netherlands (UtC) and Rafter Radiocarbon Laboratory, Lower Hutt, New Zealand (NZA). bCH = charred hazelnut shells; CC = charcoal; SH = surface-hearth; HP = hearth-pit; pit = natural or anthropogenic pit.

Table 2 Pretreatment test on CH sample from C.22 (SH.2). All treatments in hot 1% solutions for 25 min. All samples rinsed with hot distilled water after treatment and dried. # UtC- Pretreatment BP 13C ‰ 1 9692 No pretreatment 9120 ± 60 −24.4 #1 + HCl wash 2 9928 Soluble 5790 ± 50 −25.4 3 9436 Insoluble fraction after neutralization 9200 ± 90 −23.9 #3 + NaOH 4 9926 Soluble 9060 ± 50 −25.4 5 9437 Insoluble fraction after HCl rinse & neutralization 9370 ± 80 −24.3 #5 + NaOH 6 9927 Soluble 8920 ± 50 −25.3 7 9438 Insoluble fraction after HCl rinse & neutralization 9290 ± 80 −26.0 1002 M J Y Van Strydonck et al.

A

B

Figure 2 A: Floruit and 95% probability range of the dates from 45 surface-hearths dated on charred hazel- nut shells, 8 hearth-pits dated on charcoal and 3 indi- vidual charred hazelnut shells. B: Floruit and 95% probability range of the charred hazelnut shell dates compared to the typo-chronology of the lithic artifacts (Beuronian A, B, and C).

RESULTS AND DISCUSSION The 14C results together with the sample location and, if possible, the cultural association are listed in Table 1. Figure 2A above represents the floruit, or inter quartile range (Aitchison et al. 1990), and the 95% probability range of the CH and the CC dates, except for the 3 youngest CH samples which are definitely from a different period than the bulk of the measurements. Figure 2B represents the floruit and the 95% probability range of the CH dates associated with typo-chronologically well- Site of Verrebok “Dok” 1003

Figure 3 Typo-chronology for the Belgian Mesolithic according to Gob defined lithic assemblages. The classification has been done according to the typo-chronology of Gob (Figure 3 above; Gob 1981). As the analysis of the archaeological finds is still in progress and the cultural attribution of most units is not yet known, Figure 2B is made up of only 17 dates. The dates show that the CH samples (floruit: 8410-7930 cal BC, 95% probability range: 8710–7570 cal BC) and the CC samples (floruit: 7520–7280 cal BC, 95% probability range: 7600–7110 cal BC) represent two different cultural phases within the same site. The CH samples indicate that the main occupation of the site occurred during the second half of the Pre-boreal and the first half of the Boreal. All excavated concentrations seem to have been inhabited in the course of the Early Mesolithic except for three units, which apparently date back to the Late (Atlantic) Mesolithic. Recently the human presence during the Late Mesolithic has been confirmed by the discovery of some typical microliths, the so-called trapezes. The CH dates also prove that all units cannot have been in use simultaneously but rather represent diachronic visits of the site. Even the largest units seem to be the result of repeated visits. This is well illustrated by the results obtained on eight samples from unit C.14. Here six SH and two pre- sumed anthropogenic pits have been dated on CH. The results clearly demonstrate that this large unit comprises at least three different occupation phases. Similar results have been obtained for the other larger units excavated on the site. Units C.17, C.22, C.40 and C.44 all seem to have been inhabited 1004 M J Y Van Strydonck et al. at least twice during the Early Mesolithic. We strongly believe that the larger units came to existence as a result of a spatial overlapping and intersecting of some smaller units. The interpretation of the HP still poses serious problems. The measurements on CC samples from eight HP indicate that these features were in use apparently after the main occupation of the site as dated by the CH samples. This is nicely confirmed by the results of double dating on one CH and two CC samples from HP 66. It proves that, as we have stated already earlier (Crombé et al. 1999), it is rather dangerous to use hazelnut shells for dating Mesolithic HP as the former are generally residual fragments that slipped into the pit while it was dug or filled. It also proves that CC samples from HP cannot be used to date the associated lithic industry and/or artifact concentration. The 14C dates on CC samples further indicate that the site was also visited during the second half of the Boreal. However, clear prove of this has not yet been found among the archaeological finds. It could be that the remains of these occupations have not yet been excavated or that the function of the site and the activities that were performed had changed at the mid of the Boreal. Only further research can help us in solving this problem. There are indications that the 14C chronology of the site as obtained on the basis of the CH samples is in disagreement with the traditional chronology based on artifact typology (Figure 2B). In the 1970s and 1980s, various scholars worked out often contradictory typo- for the Mesolithic of the Benelux mainly based either on CC dates from HP and/or on 14C-results from for- eign areas (Crombé 1999). One of the most elaborate and refined ones has been conceived by Gob in 1981 and refined in 1990 (Gob 1990). Based on typological similarities with north European (Duv- ensee-complex) and southern German (Beuronian sequence) assemblages he proposed a diachronic model which starts with the Epi-Ahrensburgian (9700 BP–9300 BP), followed by the Beuronian A, B, C (9200 BP–8200 BP) and locally (southern Belgium) D. At Verrebroek at least three of these phases are present, namely the Beuronian A, B, and C. It should however be emphasized that, as we stated earlier (Crombé 1998a:24), a more appropriate term than “Beuronian” should be defined to indicate Early Mesolithic assemblages in Belgium. Contrary to Gob we believe that there exist only little typological similarities between the southern German Beuronian and the Belgian assemblages. If we compare the Verrebroek dates with Gob’s chronology at least two disagreements can be observed. First the Verrebroek dates point to an inversion of the Beuronian sequence with the Beu- ronian A and C as largely contemporaneous traditions and the Beuronian B as a younger one. Sec- ondly the Verrebroek dates prove that the Beuronian A-B-C sequence was most likely shorter than previously thought. According to the presently available data the Beuronian in northern Belgium ended around 8800/8750 BP.

CONCLUSION The Verrebroek-project clearly demonstrates that intensive 14C dating can contribute considerably to a better understanding of the formation processes of unstratified open-air settlements from the Early Postglacial. on CH from SH and CC from HP prove that: 1) the site has been repeatedly occupied from the second half of the Pre-boreal till the end of the Boreal (ca. 9500 BP– 8200 BP), 2) the site was incidentally visited by Late Mesolithic hunter-gatherers, 3) HP were in use after the main occupation of the site, and 4) the largest artifact concentrations are palimpsests result- ing from different diachronic visits and not, as traditionally thought, locations that were inhabited by larger groups. Site of Verrebok “Dok” 1005

ACKNOWLEDGMENTS M Landrie took care of the sample preparation and E Keppens, Vrije Universiteit Brussel, per- formed the stable isotope measurements. This research was supported by DWTC – Impulse action for research in the Belgian Federal Scientific Institutes. Archaeological research at Verrebroek was financed by the BOF – Special Research Fund of the Ghent University. We would like to thank archaeologists Yves Perdaen and Joris Sergant for their contribution to this research.

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